Mixed member voting systems are growing in popularity around the world as a method of proportional voting for determining the makeup of a legislative chamber. Under mixed member proportional systems (MMP), individuals cast two votes: one for their local district representative and one for their party of choice. This system ensures that people have representatives of their specific district or neighborhood in the legislature who should be primarily concerned with local issues and concerns. In addition to this local representation, MMP makes sure the party that has the most support nation- or region-wide also has a majority of seats in the legislature.

With MMP, a certain number of seats in the legislature are set aside for district representatives. Another set of seats is held reserved for individual parties. These seats are used as “accountability seats” to compensate for unfair and unbalanced partisan results in the district elections. Under the MMP system, voters first cast a vote for their favored local district representative. These representatives are elected under a winner-take-all system, where the candidate with a plurality of votes, regardless of party, is elected to the district’s single seat. This is the same as the current system used in the majority of elections throughout the United States. The difference emerges with the second vote, the vote for the party list. This vote is on a national or regional level with multi-seat districts. Voters cast ballots for a specific party, usually with a list of candidates, rather than for individual candidates as in the district elections. This party vote is then used to allocate the accountability seats among the various parties. In some cases, a party must win a minimum threshold of the list vote in order to be allocated seats in addition to whatever district seats it may have won. If the threshold is met, seats are divided among the parties so that the total number of seats a party holds in the legislature (the seats gained from districts won as well as the party list seats) is proportional to the percentage of the party vote won.

For many years, West Germany was the only nation to employ the use of MMP in its elections, having adopted the system after World War II. Today, however, MMP is currently in use in several countries and locations worldwide, including Scotland, Wales, and New Zealand. It has been recommended for elections in Ontario, Canada, and a modified form of MMP has also been proposed as a method for electing Britain’s House of Commons.

MMP systems have often been chosen or recommended in these locations because they allow for greater accountability and more fair representation in a legislature, particularly in a two-party electoral system. The district vote ensures that people have local representatives they can take their concerns to, representatives that are supposed to be focusing on the issues of their local constituencies. The party list vote ensures that parties are represented in the legislature proportional to the degree of support they enjoy in the broader community. Another advantage of MMP is that it encourages increased political participation among voters and candidates, including increased voter turnout and more widespread campaigning. For example, a voter may live in a district that leans heavily to a political party that he or she may not agree with, but due to the party list vote, that voter still has an opportunity to bolster his or her preferred party’s standing in the legislature. Because of this, parties and campaigns will spend more time in a greater variety of locations, rather than concentrating their time in a handful of “battleground” competitive areas and ignoring the locations that are considered to have a majority made up of any one party.

FairVote advocates that independent redistricting commissions be empowered to consider mixed member systems, also known as "districts plus" and the "Michigan Plan," as a reform to enhance non-partisan redistricting.